A color CRT includes a faceplate and a funnel which are integrally joined together, e.g., by frit sealing. The inside surface of the faceplate is covered with a phosphor screen composed of triads of phosphor elements which emit the three primary colors of light, red, green and blue when impacted by electrons. An electron gun is mounted in a neck portion of the funnel in a position remote from the faceplate. The electron gun provides three electron beams which scan the phosphor triads and cause the desired image to be produced. A shadow mask having a multiplicity of openings, or apertures, therethrough is located in proximity to the screen and is used as a color selection electrode to assure that each of the three electron beams impacts the phosphor of the proper light emitting color. Thus, for example, the electron beam which is modulated with red data impacts the phosphor elements which emit red light. Because the electrons of the beams are charged particles, the earth's magnetic field has an influence on their trajectories which can cause the electrons to impact a phosphor of the improper color, a phenomena known as misregistry. For this reason, a magnetic shield is commonly used, either in the interior or on the exterior, of the CRT, to shield a substantial portion of the electron beams trajectories from the influence of the earth's magnetic field. It is current practice to utilize an internal magnetic shield (IMS) which is attached to a shadow mask frame and extends toward the electron gun.
The magnetic effect on electron beams, which causes misregistry, occurs in the directions which are perpendicular and parallel to the longitudinal axis of the CRT. For this reason, various changes in the configuration, structure, or processing of the internal magnetic shield, the shadow mask, and the frame can beneficially influence the misregistration in one direction and adversely influence it in an orthogonal direction. Misregistry must be corrected, or minimized, in all three orthogonal field directions: axial, horizontal, and vertical. The axial (north-south) field acts parallel to the longitudinal axis of the CRT. The horizontal (east-west) field and vertical fields act along the horizontal (major) and vertical (minor) axes of the faceplate, respectively.
It is known in the art to improve the magnetic shielding characteristics of the internal components of the color CRT by annealing the components, usually within the range of 700.degree.-850.degree. C., in a non-oxidizing atmosphere, and then blacken the components, in a separate step, in an oxidizing atmosphere at a temperature of 550.degree.-600.degree. C. Alternatively, some CRT manufacturers are omitting the magnetic annealing treatment to reduce costs. However, this provides a tradeoff of cost versus performance that may be unacceptable.
An acceptable alternative, in which CRT performance is not sacrificed to reduce cost, can be achieved by the novel one-step magnetic anneal and blackening process described herein.